The present invention relates to an automatic sewing machine for sewing workpieces of different sizes, in which relative movement between a workpiece and a sewing head is controlled by a computer which receives a program according to a contour to be stitched.
In general, it is known from the manufacturing of workpieces such as shirt collars, to achieve different sizes by inserting an extending section into the middle of the collar, while the shape in the area of the collar tips remains the same.
In a technical information sheet named "IDEALNECCHI AUTOMATION FOR THE APPAREL INDUSTRY Mechanization Series Class 2001 Numerical Control Automatic Unit for producing any sewing shape" edited by the IDEAL EQUIPMENT CO. LTD., Quebeck/Canada, there is described such an automaton, in which the program for producing a stitch contour is inserted into the computer by means of punched tape. The data of the contour is determined by coordinates of some significant points which represent the variables of an algorithm applied for figuring all required values of the contour by using linear or square interpolation. Additionally, the algorithm considers besides the aforementioned variables, further information for determining the size of the contour to be sewn. In this automaton the size adjustment depending on the size adjustment of the workpiece receiving device, is manually inserted into the computer by means of appropriate push buttons at a panel. The manual input of the sizing information basically allows the operator to match the sewing contour to different workpiece sizes, with, however, accompanying disadvantages. On the one hand, sizes of garments are not standardized in such a way as to form fixed sizes to each other but, in practice, vary depending on the manufacturer. At the same time, the material of a workpiece is exposed to various influences such as for example coloring, moisture, fusing of lining etc. which cause undesired variations of the workpiece dimensions. In production, these conditions steadily require manual size adjustments according to the actual workpiece dimensions. As described above, the contour's size is manually inserted into the computer by push buttons, whereas the adjustment of the workpiece receiving elements can be set in a stepless manner. From this it may happen that a contour is not placed at the technologically required position. Such conditions may cause sewing into the fused lining of a workpiece such as a shirt collar, and this is not acceptable. Besides this disadvantage, the nonautomatic input of information into the computer is time consuming and reduces the productivity of the automaton.
It is, therefore, an object of the present invention to provide an automatic sewing machine of the above-described type with a device for detecting the size adjustment of the workpiece receiving device, in order to automatically match the size adjustment with the sewing contour controlled by the computer which controls relative motion between the workpiece and the needle of the sewing head.
Another object of the present invention is to provide a device, as described, which allows to detect the size adjustment of the workpiece-receiving device in a continuous manner.
Further objects of the present invention are to provide a device, as described, for reducing downtimes of the automaton and eliminating false data input of the machine's operator, and finally eliminating the possibility of collision between the sewing head and the workpiece receiving elements.
Still another object of the present invention is to provide a device of the foregoing character, which is simple in construction and reliable in operation.